An Imprinted Polymeric Substrate

Abstract

The present invention relates to a method for preparing a plurality of imprints on an inner surface of a polymeric substrate comprising the steps of: a) contacting a liquid polymeric mixture with a mold having an imprint forming surface thereon; b) curing the liquid polymeric mixture of step a) to form said polymeric substrate having said plurality imprints on said inner surface, when cured; and c) removing said mold from said polymeric substrate. There is also provided a method of forming the mold having the imprint forming surface thereon.

Claims

1. A method of forming a plurality of imprints on an inner surface of a polymeric substrate comprising the steps of: a) contacting a liquid polymeric mixture with a mold having an imprint forming surface thereon; b) curing the liquid polymeric mixture of step a) to form said polymeric substrate having said plurality imprints on said inner surface, when cured; and c) removing said mold from said polymeric substrate.

2. The method of claim 1, wherein said mold having said imprint forming surface thereon comprises a dissolvable material, temperature-dependent material or pressure-dependent material.

3. The method of claim 1, wherein the step of contacting said liquid polymeric mixture with said mold having said imprint forming surface thereon occurs in the presence or in the absence of an external mold.

4. The method of claim 2, wherein said dissolvable material is acrylic-based polymer, acrylate-based polymer, polystyrene or mixtures thereof.

5. The method of claim 2, wherein said temperature-dependent material is a mixture of two or more hydrocarbons having twenty to forty carbon atoms.

6. The method of claim 2, wherein said pressure-dependent material is an elastomer.

7. The method of claim 1, wherein the step of removing said mold from said polymeric substrate is undertaken in the presence of one or more solvents.

8. The method of claim 1, wherein the step of removing said mold from said polymeric substrate is undertaken in the absence of solvent.

9. The method of claim 1, the step of removing said mold from said polymeric substrate comprises the step of distorting the shape or size of said mold by subjecting said mold to a vacuum.

10. The method of claim 1, wherein said plurality of imprints on the inner surface of said polymeric substrate is a one-dimensional, two-dimensional or three-dimensional structure.

11. The method of claim 10, wherein said plurality of imprints on the inner surface of said polymeric substrate is continuous or discrete.

12. The method of claim 1, wherein said plurality of imprints on the inner surface of said polymeric substrate has a lateral dimension in the range of 20 nm to 40 nm.

13. The method of claim 1, wherein said plurality of imprints on the inner surface of said polymeric substrate has a vertical dimension in the range of 1 nm to 5 nm.

14. The method of claim 3, wherein said external mold comprises the same or different material as said mold.

15. The method of claim 1, wherein said liquid polymeric mixture comprises polymeric organosilicon compounds selected from the group consisting of polymethylhydrosiloxane (PMHS), polydimethylsiloxane (PDMS), polyethylmethylsiloxane (PEMS), polydiethylsiloxane (PDES) and blends thereof.

16. The method of claim 1, wherein the step of curing said liquid polymeric mixture is by heating or by UV irradiation.

17. A method of forming a mold having an imprint forming surface thereon, wherein said method is a nano-imprinting method, a micro-machining method or a self-assembly method.

18. The method of claim 17, wherein said nanoimprinting method comprises the steps of: i) imprinting a surface of a polymeric film; and ii) adhering the imprinted polymeric film onto an outer surface of a pre-mold, wherein the non-imprinted surface of the polymeric film is in contact with the pre-mold to thereby form said mold having an imprint forming surface thereon.

19. A polymeric substrate prepared by the method of claim 1.

20. A mold prepared by the method of claim 17.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0109] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0110] FIG. 1 shows a number of alternate methods for fabricating micro- or nano-topographies around the external surface of inner cylindrical molds; FIG. 1A is nanoimprint method with the use of a polymeric film (105) imprinted on an inner surface (103), FIG. 1B is micro-machining method and FIG. 1C is self-assembly method using the solution with micro- or nano-particles (133).

[0111] FIG. 2 shows a schematic diagram of fabrication processes for tubings; FIG. 2A is a casting or cast molding method and FIG. 2B is a dip-coating method.

[0112] FIG. 3 shows a photograph of the assembly of the acetone flow/circulation system to dissolve inner cylindrical mold (305) made of PMMA.

[0113] FIG. 4 shows a photograph of silicone tubings with micro-structures formed on the inner luminal surface. Selective surface patterning (403) or whole surface area (401) patterning can be achieved.

[0114] FIG. 5 shows a schematic diagram demonstrating the fabrication of inner cylindrical mold using specific material which melts (503) and solidifies (505) to form the mold (507).

[0115] FIG. 6 shows a schematic diagram demonstrating the solvent-less removal of inner mold (605) whereby the inner mold is heated to a certain temperature (601).

[0116] FIG. 7 demonstrates a number of alternate methods for fabricating micro- or nano-topographies around the external surface of inner cylindrical molds; FIG. 7A is nanoimprint method with the use of a polymeric film (705) imprinted on an inner surface (703), FIG. 7B is micro-machining method, FIG. 7C is self-assembly method using the solution with micro- or nano-particles (733) and FIG. 7D is the recasting of inner cylindrical mold (751) method.

[0117] FIG. 8 shows a schematic diagram demonstrating the demolding of inner elastic hollow mold (805) by vacuum.

[0118] FIG. 9 shows a number of diagrams demonstrating the possible cross-sections of gratings or lines; FIG. 9A shows the square waveform (901), FIG. 9B shows the V-grooves (903), FIG. 9C shows the U-grooves (905) and FIG. 9D shows the orientation of the tubing longitudinal axis (909) and the circumferential direction (907).

[0119] FIG. 10 shows a number of scanning electron microscope (SEM) images of 500 nm diameter pillar (protrusions-1001) arrays on the inner luminal surface of silicone tubings (FIG. 10A, scale bar of 1 μm; and FIG. 10B, scale bar of 1 μm).

[0120] FIG. 11 shows a number of scanning electron microscope (SEM) images where FIG. 11A shows the cross-sectional view of inner luminal surface (1101) of silicone tubings (1103) lined with arrays of 2 μm (microns) square microwells, scale bar of 100 nm. FIG. 11B shows the plan view of 2 μm (microns) square microwells (1105) fabricated on inner luminal surface of silicone tubings, scale bar of 1 μm.

[0121] FIG. 12 shows the silicone tubing fabricated by dip-coating method to allow thin-walled tubing fabrication (left image), while the image on the right is an expanded view of the selected section of the image on the left showing patterns of 10 μm (microns) microwells of circular shape (1203) in a hexagonal array (1201).

[0122] FIG. 13 shows a number of scanning electron microscope (SEM) images indicating examples of hierarchical structures or multilevel three-dimensional (3D) structures which can be fabricated on flat films by nanoimprint lithography; FIG. 13A shows gratings (1301) that are aligned perpendicular to the larger trough-like (1303) structures, scale bar of 1 μm and FIG. 13B shows microwells in circular shapes (1305) and trough-like (1307) structures, scale bar of 1 μm.

[0123] FIG. 14 shows a photograph of an acetone bath (1401) containing the tubing with dissolvable inner mold (1403).

DETAILED DESCRIPTION OF DRAWINGS

[0124] Referring to FIG. 1, FIG. 1A shows a schematic diagram of the nanoimprint method with the use of a two-dimensional (2D) flat master mold (101) to create micro- or nano-topographies (111) on the inner luminal surfaces of a polymeric film (103). The desired topographies were imprinted onto a thin freestanding polymer film (113). The imprinting temperature is above the glass transition temperature of the polymer film. The imprinted sheet (105) was adhered around a cylinder or polymer rod (107) by tape adhesive to form the polymer rod with the negative micro- or nano-structures on the outer surface (109). In this case, the cylindrical mold and adhesive must be dissolvable by the solvent in which the tubing is chemically resistant to. FIG. 1B shows a schematic diagram of the micro-machining method where the polymer cylinders (121) are directly machined by techniques such as but not limited to laser milling, micro-EDM or micro-milling to create micro- or nano-patterns (123 or 125) on the polymer rod (outer or external) surface. The techniques selectively remove material from defined positions on the cylinder external surface to create the desired micro- or nano-patterns (123 or 125). Such techniques enable the fabrication of seam-less patterning around the circumference of the rod. FIG. 1C shows a schematic diagram of the self-assembly method where the micro- or nano-topographies (135) can be achieved via the deposition of micro- or nano-particles (137) from a solution of micro- or nano-particles (133) onto the rod or cylindrical mold (131) by drawing a meniscus of micro- or nano-particle suspension along the length of the rod.

[0125] Referring to FIG. 2, FIG. 2A shows a schematic diagram of the casting or cast molding method where the liquid polymer (205) is cast to form the tubing into a mold, which comprises of two concentric layers whereby the inner layer is the patterned inner cylindrical mold (201), and the outer layer (203) is a tube that can be easily removed after the liquid polymer has cured. This outer layer can be peeled away or be dissolved by a solvent which the tubing is chemically resistant to. The liquid polymer is degassed (207) to remove bubbles and is cured either by heat or UV (209). The outer layer (203) is removed from the mold by dissolving it or peeling it away. The patterned inner cylindrical mold (201) is also removed by dissolving it, to form the micro- or nano-patterning (211) on the inner surfaces (213) of the tubes, whereas the outer surface (215) of the tubes does not have the micro- or nano-patterning. FIG. 2B shows a schematic diagram of the dip-coating method where the cylindrical mold or rod with the negative structures (221) is vertically dipped into the liquid pre-polymer mix (223). The cylindrical mold is then removed from the liquid polymer where the excess liquid polymer is allowed to drain away, leaving a thin layer of liquid polymer (227) on the mold surface. The liquid polymer is cured either thermally or under UV exposure (225). The dipping (229) and curing (231) steps are repeated to achieve the required wall thickness (233) of the tubing. The patterned inner cylindrical mold (221) is also removed by dissolving it to form the micro- or nano-patterning (235) on the inner surfaces (237) of the tubes, whereas the outer surface (239) of the tubes does not have the micro- or nano-patterning.

[0126] Referring to FIG. 3, FIG. 3 shows a photograph of the system that is connected to a peristatic pump (301) and an acetone reservoir (303) via silicone tubings to dissolve the inner cylindrical mold (305), where the solvent was pumped through the mold assembly and circulated continuously till the inner mold was dissolved. The used solvents in the reservoir can be further exchanged with fresh solvents to maintain the effective rate of dissolution. This method will allow faster dissolution of the inner mold and allow for fabrication of longer tubes.

[0127] Referring to FIG. 4, FIG. 4 shows a photograph of silicone tubings with micro-structures formed on the inner luminal surface where the selective surface patterning (403) or whole surface area (401) patterning can be achieved.

[0128] Referring to FIG. 5, FIG. 5 shows a schematic diagram of casting the inner cylindrical mold (507) using specific material which melts (503) and solidifies (505) to form the mold (507). By using existing tubings (e.g. silicone) (501) with micro- or nano-topographies on the inner luminal surface, the inner cylindrical mold (507) can be casted with a compound or solution (503). This compound or solution can be heated to melt into a liquid state (503) and solidify back (505) when the temperature is reduced. An example is paraffin wax. It is a solid at room temperature and has melting points ranging from about 48° C. to 70° C. depending on the grade of chain length of the hydrocarbon. When heated, the wax melts into a liquid and can be casted into the existing tubings (501) to form the inner cylindrical mold (507). Upon reduction in the temperature, the wax solidifies back and conforms to the shape of the tubing including the micro- or nano-topographies (509). After demolding, the wax inner cylindrical mold can be further used for casting new tubings.

[0129] Referring to FIG. 6, FIG. 6 shows a schematic diagram of the solvent-less removal of inner mold (603) whereby the whole assembly will be heated to a certain temperature (601), typically is the temperature above the melting point or the vaporizing temperature of the inner mold material to melts or vaporizes away the inner mold (605). In the case of wax, the assembly can be heated above 50° C. to melt away the wax. The remaining tubings would have the micro- or nano-patterns (607) imprinted on.

[0130] Referring to FIG. 7, FIG. 7A shows a schematic diagram of the nanoimprint method with the use of a two-dimensional (2D) flat master mold (701) to create micro- or nano-topographies (711) on the inner luminal surfaces of a polymeric film (703). The desired topographies were imprinted onto a thin freestanding polymer film (713). The imprinting temperature is above the glass transition temperature of the polymer film. The imprinted sheet (705) was adhered around a cylinder or polymer rod (707) by tape adhesive to form the polymer rod with the negative micro- or nano-structures on the outer surface (709). In this case, the cylindrical mold and adhesive must be dissolvable by the solvent in which the tubing is chemically resistant to. FIG. 7B shows a schematic diagram of the micro-machining method where the polymer cylinders (721) are directly machined by techniques such as but not limited to laser milling, micro-EDM or micro-milling to create micro- or nano-patterns (723 or 725) on the polymer rod surface. The techniques selectively remove material from defined positions on the cylinder external surface to create the desired micro- or nano-patterns (723 or 725). Such techniques enable the fabrication of seam-less patterning around the circumference of the rod. FIG. 7C shows a schematic diagram of the self-assembly method where the micro- or nano-topographies (735) can be achieved via the deposition of micro- or nano-particles (137) from a solution of micro- or nano-particles (733) onto the rod or cylindrical mold (731) by drawing a meniscus of micro- or nano-particle suspension along the length of the rod. FIG. 7D shows a schematic diagram of the recasting of inner cylindrical mold (751) method, where the negative relief structures of the desired micro- or nano-topographies (753) can be fabricated onto an elastic and hollow cylindrical mold (e.g. silicone) (751). The existing silicone tubings with the desired micro- or nano-topographies (753) on the inner luminal surface can also serve as a mold in fabricating a “daughter” hollow inner cylindrical mold (751). In the case, the mold (which is the existing silicone tubing) must be larger in diameter than the “daughter” mold. The space is then filled with the liquid polymer (755) and upon the curing and demolding steps; the “daughter” mold would contain the desired micro- or nano-topographies (753) from the existing silicone tubings.

[0131] Referring to FIG. 8, FIG. 8 shows a schematic diagram demonstrating the demolding of inner elastic hollow mold (805) by vacuum, where the key process is the use of vacuum and the elasticity of the inner cylindrical mold to demold from the formed tubings (801). To remove the inner elastic mold (805), one end of the inner hollow mold is sealed and the other end of the inner hollow cylindrical mold is connected to a vacuum source. The pressure of the air (803) inside the elastic hollow cylindrical mold is reduced relative to the atmospheric pressure. This causes the hollow mold (805) to collapse within the tubings. The collapse of the inner mold (805) will effectively demold the hollow inner mold from the inner tubings walls and allow the inner mold to be removed from the inner space of the tubings. Due to the elastic nature of the hollow inner mold, the mold can be reused to cast for another piece of tubings after the vacuum is released.

[0132] Referring to FIG. 9, FIG. 9A shows the cross-section view of the square waveform (901) which is one of the line grating features. FIG. 9B shows the cross-section view of the V-grooves (903) and FIG. 9C shows the cross-section view of the U-grooves (905) which are part of the line grating features. FIG. 9D shows that the lines grating can orientate parallel to the tubing longitudinal axis (909), perpendicular (circumferential direction-907), or diagonally.

[0133] Referring to FIG. 10, FIG. 10A and FIG. 10B show a number of scanning electron microscope (SEM) images of the two-dimensional (2D) micro- or nano-structures that include regular arrays of protrusions (posts/pillars) and this is demonstrated by the 500 nm diameter pillar (protrusions-1001) arrays on the inner luminal surface of silicone tubings.

[0134] Referring to FIG. 11, FIG. 11 shows a number of scanning electron microscope (SEM) images of the two-dimensional (2D) micro- or nano-structures that include wells (pits), where FIG. 11A shows the cross-sectional view of inner luminal surface (1101) of silicone tubings (1103) lined with arrays of 2 μm (microns) square microwells. FIG. 11B shows the plan view of 2 μm (microns) square microwells (1105) fabricated on inner luminal surface of silicone tubings.

[0135] Referring to FIG. 12, FIG. 12 shows a number of images of the two-dimensional (2D) micro- or nano-structures that include micro-wells structures in the shape of circles, where the image on the left shows the silicone tubing (1205) fabricated by dip-coating method to allow thin-walled tubing fabrication, and the image on the right is the expanded view of the selection section from the image on the left, showing patterns that consist of 10 μm (microns) microwells of circular shape (1203) in a hexagonal array (1201).

[0136] Referring to FIG. 13, FIG. 13 shows a number of scanning electron microscope (SEM) images of hierarchical or multi-level three-dimensional (3D) structures, which can be fabricated on flat films by nanoimprint lithography, where FIG. 13A shows gratings (1301) that are aligned perpendicular to the larger trough-like (1303) structures and FIG. 13B shows microwells in circular shapes (1305) and trough-like (1307) structures.

[0137] Referring to FIG. 14, FIG. 14 shows a photograph of an assembly being immersed in a container of solvent which is capable of dissolving the inner cylindrical mold completely, where the container of solvent is an acetone bath (1401) containing the tubing with dissolvable inner mold (1403).

EXAMPLES

[0138] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

List of Abbreviations Used

[0139] H: hour(s)

[0140] m.p.: melting point

[0141] min: minute(s)

[0142] FDTS: perfluorodecyltrichlorosilane

[0143] PDMS: polydimethylsiloxane

[0144] PMMA: polymethylmethacrylate

[0145] PTFE: polytetrafluoroethylene (Teflon)

[0146] PS: polystyrene

[0147] Rt: room temperature

[0148] UV: ultraviolet irradiation

Materials and Methods

[0149] Poly(dimethylsiloxane) or PDMS (under trademark Sylgard® 184) was provided by the Dow Chemical Company (Midland, Mich., United States). Acetone and chloroform were purchased from Merck (Kenilworth, N.J., United States of America) and used without further purification, unless specified otherwise. Polymethylmethacrylate (PMMA) free-standing films were obtained from Goodfellow Cambridge Ltd. (United Kingdom). Perfluorodecyltrichlorosilane (FDTS) was purchased from Gelest Inc. (Morrisville, Pa., United States of America). Other reagents or materials and/or solvent(s) than the above were purchased from Sigma-Aldrich Corp. (St. Louis, Mo., United States of America) and were used as received where otherwise noted in the experimental text below.

Example 1—‘Solvent Dissolution of Dissolvable Mold’ Method

[0150] The method of imparting micro- or nano-topographies on the curved, inner surface of the tubing involves creating a negative of the desired topographies on the outer surface of a dissolvable cylinder or polymer rod which can be dissolved by a solvent in which the tubing is chemically resistant to. The tubing can be formed by cast molding or dip-coating, with the patterned cylinder serving as a template for the inner surface of the tubing. Discrete topographies in addition to continuous topographies (e.g. lines), can be created using this method.

##STR00001##

[0151] The following describes the sequential process that must be followed for the creation of the tubing:

1. Method to Create a Negative Relief of the Desired Topographies onto a Cylindrical Mold

[0152] This step enables the fabrication of the negative micro- or nano-features onto the cylindrical inner mold. The cylindrical inner mold can be a rod or a hollow tube. The hollow tube version allows solvents to be pumped and circulated through the inner mold and enhanced dissolution rate of the mold. The entire dissolvable inner mold embodiment must be dissolvable in the solvent. The cylindrical mold can be fabricated by nano-imprint, micro-machining or self-assembly methods as indicated in FIGS. 1A-1C.

A) Nanoimprinting Method

[0153] The imprinting method allows two-dimensional (2D) flat master molds (101) to be used to create micro- or nano-topographies (111) on curved inner luminal surfaces (103). The desired topographies were first imprinted onto a thin freestanding polymer film (113) that can be dissolved by a solvent in which the tubing material is chemically resistant to. Imprinting temperature is above the glass transition temperature of the polymer film (FIG. 1A).

B) Micro-Machining Method

[0154] Polymer cylinders (121) are directly machined by techniques such as but not limited to laser, micro-EDM or micro-milling to create micro- or nano-patterns (123 or 125) on the polymer rod surface (FIG. 1B). The techniques selectively remove material from defined positions on the cylinder external surface to create the desired micro- or nano-patterns (123 or 125). Such techniques enable the fabrication of seam-less patterning around the circumference of the rod.

C) Self-Assembly of Organic or Inorganic Micro- or Nano-Spheres

[0155] Micro- or nano-topographies (135) can also be achieved via the deposition of particles (e.g. PS, PMMA, silica-137) onto the tubes or rods by drawing a meniscus of particle suspension from the solution with micro- or nano-particles (133) along the length of the rod (131) (FIG. 1C). This can result in either closely packed or loosely packed particles depending on the type of solvents and surfactants used. After the tube is molded, the particles can be dissolved in the same solvent as the rod (e.g. PS/PMMA can dissolve in acetone), or in a different solvent (e.g. silica can dissolve in sodium hydroxide).

2. Methods of Fabricating Tubings with Patterned Inner Surface

[0156] The inner cylindrical mold serves as the template for the fabrication of tubings. The tubings can be fabricated via two processes: casting or dip-coating. The diameter of the inner cylindrical mold defines the inner diameter of the tubings. The tubings' wall thickness and external diameter can be controlled by the outer cylindrical mold (casting method—FIG. 2A) or by the number of dips (dip-coating method—FIG. 2B).

A) Casting or Cast Molding Method

[0157] In the cast molding method, the external cylindrical mold (203) defines the external diameter of the tubing (FIG. 2A). The external cylindrical mold can be made of various polymers, which include but not limited to polyethylene, polystyrene, polycarbonate, polymethylmethacrylate, polypropylene, and polytetrafluoroethylene. The external cylindrical mold can also be made of metal or glass or ceramics. External cylindrical molds may be coated with a layer of anti-stiction coatings such as PTFE (Teflon) or perfluorodecyltrichlorosilane (FDTS) to reduce adhesion between the tubings and the external mold, and facilitate demolding. The material used in the external cylindrical mold must not deform at the temperature used for curing the polymer of the tubings. In the case of UV-curable tubing material, the external cylindrical mold can be UV-transparent.

Sequential Process of the Casting or Cast Molding Method is as Follows:

[0158] I. Casting the liquid polymer (e.g. PDMS-205) forming the tubing into a mold which comprises of two concentric layers whereby the inner layer is the patterned inner cylindrical mold (201), and the outer layer (203) is a tube that can be easily removed after the liquid polymer has cured. This outer layer (203) can be peeled away or be dissolved by a solvent which the tubing is chemically resistant to. The inner layer of the mold determines the inner diameter and surface of the tubing while the outer layer defines the outer diameter and surface of the tubing.

[0159] II. Degassing the liquid polymer to remove bubbles (207).

[0160] III. Curing the liquid polymer either by heat or UV (209). Curing conditions vary according to the temperature used. However, the curing temperature of the tubing polymer should be less than the glass transition temperature of the inner and outer mold. If curing temperature is higher than the glass transition temperature of the inner mold, the micro- or nano-topographies may be deformed.

[0161] IV. Removing the outer layer (203) of the mold by dissolving it or peeling it away.

B) Dip-Coating Method

[0162] I. Dipping the cylindrical mold (rod with the negative structures) (221) vertically into liquid pre-polymer mix (e.g. PDMS) (223) (FIG. 2B).

[0163] II. Removing the cylindrical mold from the liquid polymer and allow excess liquid polymer to drain away leaving a thin layer of liquid polymer (227) on the mold surface.

[0164] III. Curing the liquid polymer either thermally or under UV exposure (225).

[0165] IV. Repeating the dipping and curing steps (I)-(III) to achieve the required wall thickness (233) of the tubing.

3. Methods for Dissolving Inner Mold

[0166] We disclose two processes which can be used to dissolve the inner cylindrical mold using a solvent such as acetone after the curing of the tubing material. After the inner mold was dissolved, the tubings can be rinsed with ethanol and IPA to remove the solvent.

A) Solvent Bath Method

[0167] The assembly was immersed in a container of solvent capable of dissolving the inner cylindrical mold completely. In the case of PMMA or PS material, acetone is used. The bath can be heated above room temperature and stirred constantly to accelerate dissolution of the inner mold (FIG. 14).

B) Solvent Pump-Through/Circulation Method

[0168] In this method, a hollow cylindrical mold was used in the tubing fabrication to allow solvent flow-through. The assembly was connected to a peristatic pump (301) and solvent reservoir (303) via silicone tubings. Solvent was pumped through the mold assembly and circulated continuously till the inner mold (305) was dissolved (FIG. 3). The used solvents in the reservoir can be further exchanged with fresh solvents to maintain the effective rate of dissolution. This method will allow faster dissolution of the inner mold and allow for fabrication of longer tubes.

Example 2—Silicone Tubings Fabrication by Casting Method

[0169] For the current prototype, a nickel mold was used to imprint on polymethylmethacrylate (PMMA) films with thickness of 0.05 mm via a batch imprinter system at elevated temperature and pressure. The conditions used for imprinting is: 120 to 150° C., 40 bars, and 300 to 600 seconds. These films can also be fabricated in a high-throughput manner via other imprinter systems such as roll-to-roll imprinter and roll-to-plate imprinter. The imprinted sheet/film was then adhered around a cylinder (e.g. PMMA or PS) by tape adhesive (e.g. acrylic tape). The adhesive can also be liquid adhesive or a solvent adhesive for acrylics such as chloroform. The cylindrical mold and adhesive must be dissolvable by the solvent in which the tubing is chemically resistant to.

[0170] As mentioned above, micro or nano-topographies were transferred from a nickel or silicon master mold onto freestanding thin PMMA films (0.05 mm thick) by nanoimprinting lithography or hot embossing process. The nanoimprinting process was performed at 150° C., 40 bars, 600 seconds. The films were demolded at 30° C. The imprinted PMMA films were wrapped around the circumference of the PMMA hollow cylinder (6 mm in diameter) to form the inner dissolvable mold. The PMMA film was adhered to the cylinder by acrylic-based double-sided tape. The assembly of the mold for casting the tubings is formed by using an outer cylindrical mold (polystyrene drinking straw; 10 mm in diameter) which defines the external diameter of the tubing and an inner dissolvable mold which defines the inner diameter. The inner dissolvable mold is secured in the center of the outer hollow mold by blue-tack. The blue-tack holds the inner mold along the center axis relative to the external mold. The mold assembly was left upright. Sylgard 184 was prepared in the ratio of 1:10 (curing agent:pre-polymer mix) by weight. Silicone pre-polymer mixtures were then poured into the spaces between the inner and outer mold. The mixtures were degassed in a vacuum desiccator to remove bubbles in the mix for 1 to 2 hours with the assembly standing upright. The assembly with the silicone mix was then cured thermally at 80° C. curing temperature over a period of 18 hours. After curing, the outer mold was peeled away.

[0171] Selective surface patterning (403) or whole surface area (401) patterning can be achieved using the method disclosed herein as indicated in FIG. 4.

Example 3—‘Solvent-Less Removal of Inner Cylindrical Mold’ Method

[0172] The key feature of this method is the use of an inner mold material which melts or vaporizes after increasing the temperature to above the material's melting or sublimation temperature.

##STR00002##

1. Fabrication of Inner Cylindrical Mold by Casting of a Material

[0173] Using existing tubings (e.g. silicone) with micro- or nano-topographies (501) on the inner luminal surface, the inner cylindrical mold can be casted with a compound or solution. This compound or solution can be heated to melt into a liquid state and solidify back when the temperature is reduced. An example is paraffin wax. It is a solid at room temperature and has melting points ranging from about 48° C. to 70° C. depending on the chain length of the hydrocarbon. When heated, the wax melts into a liquid (503) and can be casted into the existing tubings to form the inner cylindrical mold. Upon reduction in the temperature, the wax solidifies (505) back and conforms to the shape of the tubing including the micro- or nano-topographies (509). After demolding, the wax inner cylindrical mold (507) can be further used for casting new tubings (FIG. 5).

2. Methods of Fabricating Tubings with Patterned Inner Surface

[0174] With the inner cylindrical mold, tubings can be casted using similar methods described previously such as dip-coating and casting. UV-curable resins can be used in placed of thermally-cured resins in this case. An example is UV-curable polydimethylsiloxane (silicone-based) material.

3. Methods for Removing Inner Mold

[0175] The removal of the inner mold does not require any solvent. The whole assembly will be heated (6010) above the melting or vaporizing temperature of the inner mold material to melt or vaporize away the inner mold (605). In the case of paraffin wax, the assembly can be heated above 50° C. to melt away the wax. The temperature will not melt the silicone tubing material, which has a high degradation temperature (FIG. 6).

Example 4—‘Tubing Fabrication and Vacuum-Assisted Demolding’ Method

[0176] This method is used to fabricate tubings with micro- or nano-topographies on the inner luminal surface. However, this method is independent from the other two methods described above. This method comprises of the following main processes:

##STR00003##

1. Method to Create a Negative Relief of the Desired Topographies onto an Elastic and Hollow Cylindrical Mold

[0177] Negative relief structures of the desired micro- or nano-topographies can be fabricated onto an elastic and hollow cylindrical mold (e.g. silicone) (751) by nanoimprint lithography method (FIG. 7A), micro-machining method (FIG. 7B) or self-assembly method (FIG. 7C) as previously described. The silicone tubings with the desired micro- or nano-topographies (753) on the inner luminal surface can also serve as a mold in fabricating “daughter” hollow inner cylindrical mold (FIG. 7D). In this case, the silicone tubings (acting as a mold) must be larger in diameter than the “daughter” mold.

2. Methods of Fabricating Tubings with Patterned Inner Surface

[0178] Processes for fabricating the tubings are similar to methods previously described which include casting and dip-coating methods.

3. Method to Demold by ‘Vacuum-Assisted’ Technique

[0179] The key process is the use of vacuum in conjunction with the elasticity of the inner cylindrical mold to demold from the formed tubings (801). After the tubings are cured around the inner and outer cylindrical molds, the outer mold can be peeled away physically. To remove the inner elastic mold, one end of the inner hollow mold is sealed and the other end of the inner hollow cylindrical mold is connected to a vacuum source (FIG. 8). The pressure of the air (803) inside the elastic hollow cylindrical mold is reduced relative to the atmospheric pressure. This causes the hollow mold (805) to collapse within the tubings. The collapse of the inner mold will effectively demold the hollow inner mold from the inner tubings walls and allow the inner mold to be removed from the inner space of the tubings. Due to the elastic nature of the hollow inner mold, the mold can be reused to cast for another piece of tubings after the vacuum is released.

Example 5—Types of Micro- or Nano-Topographical Surfaces

[0180] The types of micro- or nano-topographical features which can be replicated on the inner luminal surface of tubings include continuous one-dimensional (1 D) patterns, discrete two-dimensional (2D) arrays, and three-dimensional (3D) hierarchical structures. Micro- or nano-topographical features which can be fabricated or replicated by nanoimprint lithography, micro-machining techniques or self-assembly can potentially be transferred to the inner luminal surface of the tubings via the method as defined above. The patterns can be ordered arrays, non-ordered meta-surfaces or random (e.g. random roughness). Lateral and vertical dimensions of the features can go down to 30 nm and 2 nm respectively depending on the formulation of the tubing polymer.

Continuous Structures (One-Dimensional Structures)

[0181] Continuous or line grating features can include the cross-sections such as square waveform (901), V-grooves (903) and U-grooves (905) as shown in FIGS. 9A-9C. The lines grating can orientate parallel to the tubing longitudinal axis (909), perpendicular (circumferential direction) (907), or diagonally as shown in FIG. 9D.

Discrete Protrusion or Well Structures (Two-Dimensional Structures)

[0182] Two-dimensional (2D) micro- or nano-structures can include regular arrays of protrusions (posts/pillars) (1001) (FIGS. 10A-10B) or wells (pits). The posts and wells structures can be in variety of shapes (include but not limited to circles (1203), squares (1105), triangles) as shown in FIGS. 11A-11B. The arrangement of wells or protrusions can include but not limited to hexagonal arrays (1201) (FIGS. 12A-12B) or square arrays.

Hierarchical or Multilevel Structures (Three-Dimensional Structures)

[0183] Hierarchical or multilevel three-dimensional (3D) structures can be replicated on the inner luminal surface. A two-steps imprinting process can be performed on flat free-standing polymer films to achieve hierarchical micro- or nano-structures. Some examples of hierarchical or multilevel three-dimensional mold structures include the following as shown in FIGS. 13A-13B.

High Aspect Ratio Features

[0184] Micro- or nano-protrusions or wells with high aspect ratio more than 1 can potentially be fabricated on the inner luminal surface. The method disclosed herein does not require physical demolding of the inner mold from the tubings. Therefore, this method is advantageous in minimizing physical damage and preserves the high aspect ratio structures.

INDUSTRIAL APPLICABILITY

[0185] The imprinted polymeric substrate prepared by the method as defined above may be used generally in hydraulic applications. Hence, the polymeric substrate may be used as superhydrophobic tubings with reduced friction, tubings with enhanced passive mixing or tubings with anisotropic wetting structures that promote flow. The polymeric substrate prepared by the method as defined above may be used in medical applications. Hence, the polymeric substrate may be used as blood-handling tubings with reduced hemolysis, catheters with reduced biofouling or ultrasound-guided catheters with enhanced ultrasound visibility.

[0186] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.